It is known that ultra-violet radiation from the sun can cause acute adverse effects such as premature aging of skin and discoloration. Over a period of years, skin exposed to the sun may become permanently darker than the other unexposed skin, sun spots and areas of hyper pigmentation may also occur. A “tan” is essentially the skin's way of increasing its defense against the onslaught of damaging ultra-violet light. Tanning protects against sun damage principally by Increasing the melanin content of the epidermis. It is well known that light radiation of wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that irradiation of wavelengths of from 280 to 320 nm. i.e., UV-B, causes erythema and burning of the skin. Melanin which is basically responsible for skin pigmentation is synthesized by melanocytes, a cell type present at dermis-epidermis junction, from an amino acid tyrosine. Tyrosine is acted upon by an enzyme tyrosinase which is the key enzyme in melanogenesis, free radicals are necessary for this reaction, however free radicals can cause skin cell damage.
Conventional skin lightening compositions are based on sunscreens which maintain skin color against ultra-violet light. They have been based on materials which absorb/block incident ultra-violet light of the wavelength which produces the tanning of the skin. Sunscreens alone cannot lighten the skin significantly and their action on the skin is only to reduce the ingress of incident ultra-violet into the skin and is therefore effective only during the day. Other approaches have been to use skin lightening agents which are believed to control dispersion of melanosomes or inhibit tyrosinase.
Sebum is produced in the skin adds a protective oil layer that protects the skin and contributes to the retention of moisture in the skin. It provides a natural glow and sheen to the skin. Modern cleansing with detergents removes the natural oil layer on the skin.
Patent GB 1 533 1 19 discloses cosmetic composition having a combination of niacinamide and a mixture of UV absorbers, which absorb in the UV range of 290 nm to 360 nm. IN 169917 discloses the use of a silicone compound to synergistically enhance skin lightening benefits obtained from the combination of niacinamide and sunscreens. Patent IN 172889 discloses the use of titanium dioxide at levels from 3% along with octyl methoxy cinnamate to provide protection from excessive exposure to ultra-violet fays over a broad range of wavelengths in the UV-A and UV-B regions. U.S. Pat. Nos. 5,997,887 and 5,997,890 disclose topical compositions comprising pigmentary grade particulate material such as titanium dioxide, with a particle size greater than 100 nm to about 300 nm along with an active vitamin B3 useful for imparting an essentially immediate visual improvement in skin appearance. Vitamin C has been shown to help with skin damage resulting from exposure to the sun. (Farris, P K, Dermatol. Surg. 2005 July; 31(7 Pt 2):814-7).
Kojic acid has also been described to lighten skin and reduce tanning. (U.S. Pat. No. 4,278,656). Astaxanthin due to its antioxidant properties may also protect skin and provide desired coloration. (H. Corrales Padilla, et al., Int. J. Dermatol. 13(5):276-282 (1974); D. Jimenez, et al. Allergol. et Immunopathol. 15(4):185-189 (1987)).
The stratum corneum of skin poses a barrier to transmission of active ingredients of topical compositions into the layers of the skin. Milled particles, i.e. particles of less than 500 nm of different sizes, have been shown to penetrate layers of the skin for topical compositions. (Dermatoendocrinol. 2009 July-August; 1(4): 197-206). A possible route for entry of topically applied agents is through microchannels between the cells of the stratus corneum. (Verma and Fahr, Eur. J. Pharm. Biopharm 2003:55:271-277).
Despite the development of skin compositions, there is an ongoing need to provide effective and safe compositions for conditioning and improving the appearance of skin.